Biomedical subjects

Matthias Muller

Publications and source records attributed to Matthias Muller.

4 recordsLinked to original sources

PubMed2007

MALDI-TOF MS in lipidomics.

So far, matrix-assisted laser desorption and ionization time-of-flight mass spectrometry (MALDI-TOF MS) seemed to be nearly a synonym for protein analysis. However, there is growing evidence that this technique is also an useful tool in lipid analysis and lipidomics because of its fast, simple and convenient performance allowing to record mass spectra of cells, crude tissue or body fluid extracts or even intact tissue slices in a few minutes. On the negative side, however, the reproducibility of MALDI-TOF mass spectra depends significantly on the homogeneity of the co-crystals between matrix and analyte and different lipid classes are detected with different sensitivities. This is especially important because lipids with quaternary ammonia groups (e.g., GPCho) may prevent the detection of other lipid classes (e.g., GPEtn). This review starts with a short overview on traditional methods of lipid analysis with the focus on mass spectrometric methods and compares MALDI-TOF MS with other important ionization techniques. Afterwards, some landmarks in the development of MALDI-TOF MS will be introduced and some important examples in the field of tissue and body fluid lipid analysis will be discussed. This review ends with a short outlook and summary focusing on the advantages and drawbacks of MALDI-TOF MS in lipidomics.

Complex Mixtures↗

PubMed2003

Ligand crowding at a nascent signal sequence.

We have systematically analyzed the molecular environment of the signal sequence of a growing secretory protein from Escherichia coli using a stage- and site-specific cross-linking approach. Immediately after emerging from the ribosome, the signal sequence of pOmpA is accessible to Ffh, the protein component of the bacterial signal recognition particle, and to SecA, but it remains attached to the surface of the ribosome via protein L23. These contacts are lost upon further growth of the nascent chain, which brings the signal sequence into sole proximity to the chaperone Trigger factor (TF). In its absence, nascent pOmpA shows extended contacts with L23, and even long chains interact in these conditions proficiently with Ffh. Our results suggest that upon emergence from the ribosome, the signal sequence of an E. coli secretory protein gradually becomes sequestered by TF. Although TF thereby might control the accessibility of pOmpA's signal sequence to Ffh and SecA, it does not influence interaction of pOmpA with SecB.

Bacterial Outer Membrane Proteins↗

PubMed2002

The integration of YidC into the cytoplasmic membrane of Escherichia coli requires the signal recognition particle, SecA and SecYEG.

The integration of the polytopic membrane protein YidC into the inner membrane of Escherichia coli was analyzed employing an in vitro system. Upon integration of in vitro synthesized YidC, a 42-kDa membrane protected fragment was detected, which could be immunoprecipitated with polyclonal anti-YidC antibodies. The occurrence of this fragment is in agreement with the predicted topology of YidC and probably encompasses the first two transmembrane domains and the connecting 320-amino acid-long periplasmic loop. The integration of YidC was strictly dependent on the signal recognition particle and SecA. YidC could not be integrated in the absence of SecY, SecE, or SecG, suggesting that YidC, in contrast to its mitochondrial orthologue Oxa1p, cannot engage a SecYEG-independent protein-conducting channel.

Adenosine Triphosphatases↗

PubMed2001

Direct interaction of YidC with the Sec-independent Pf3 coat protein during its membrane protein insertion.

YidC is a newly defined translocase component that mediates the insertion of proteins into the membrane bilayer. How YidC functions in the insertion process is not known. In this study, we report that the Sec-independent Pf3 coat protein requires the YidC protein specifically for the membrane translocation step. Using photocrosslinking techniques and ribosome-bound Pf3 coat derivatives with an extended carboxyl-terminal region, we found that the transmembrane region of the Pf3 coat protein physically interacts with YidC and the bacterial signal recognition particle Ffh component. We also find that in the insertion pathway, Pf3 coat interacts strongly with YidC only after its transmembrane segment is fully exposed outside the ribosome tunnel. Interaction between Pf3 coat and YidC occurs even in the absence of the proton motive force and with a Pf3 coat mutant that is defective in transmembrane insertion. Our study demonstrates that YidC can directly interact with a Sec-independent membrane protein, and the role of YidC is at the stage of folding the Pf3 protein into a transmembrane configuration.

Bacterial Proteins↗